Various prior art devices exist for modifying the tonal qualities of electronic signals. In audio frequency applications, the types of signals processed can be speech, musical instruments, synthesized waveforms, and the like. Prior art devices for processing musical instrument signals generally have a very limited ability to provide the musician with a variety of tonal qualities in the resulting sound. For example, prior art circuits exist for processing electric guitar signals that have a singular tonal quality, or “sound”. This is a serious limitation, since the guitarist must frequently employ a plurality of different circuits if different “sounds” are desired.
Some schemes exist in the art that include circuits with more than a singular sound. Usually this involves adding additional active circuits that the guitarist can activate, as desired. While such an arrangement can be successful, it also results in much greater total component count and added expense.
In addition, in some applications, it is desirable to deliberately add distortion to the sound to affect the tonal qualities. For example, deliberately adding distortion to the sound of an electric guitar began in the 1950's when rock music was becoming popular. At this time, the only techniques that an electric guitarist has to increase the amount of distortion into his sound was to increase the volume of a vacuum tube amplifier by (1) picking the strings of the guitar harder, (2) turning the volume of the guitar higher, or (3) turning the volume of the amplifier up; or some combination or variation of all three techniques. However, these techniques have the drawbacks that the guitarist usually could still not achieve the desired level of distortion, and/or high sound pressure levels were created that many people find uncomfortable or even distressing.
During the 1960's, the characteristic sound of an overdriven vacuum tube amplifier was realized while playing at lower volumes by using new types of circuits. These new circuits were frequently called “fuzzboxes” and were separate boxes that were external to the amplifier. Fuzzboxes typically employed a cascade or series connection of two or more transistor amplifier gain stages that had high input-to-output gain and that were easily overdriven by the output signal from the guitar. This provided a favorable increase in distortion and sustain to the guitar sound. However, it also introduced a new quality to the sound that is disliked by many guitarists. This quality is often referred to as the “solid-state sound” or the “transistor sound”. Either of these terms has acquired a very negative connotation to many guitarists. That is, the solid-state or transistor sound is quite different than the “tube sound”, which was developed by the overdriven vacuum tube amplifiers.
Many guitarists continue to believe that the best distortion sounds come from amplifiers that employ tube circuits. While the best solid-state amplifiers come close, they are frequently considered to be inferior to the tube amplifiers. Despite the many solid-state amplifiers that have been developed and introduced to the marketplace since the 1960's, the solid-state sound is still not on par with that of the tube amplifiers. Indeed, many different schools of thought exist on why there are differences in the sound and feel between the solid-state and tube amplifiers. Recent attempts to emulate the sound and feel of tube amplifiers have stagnated.
It has been an objective in the guitar industry for many years to develop solid-state amplifiers that have the sound and feel of the overdriven tube amplifier. “Feel” indicates that a tube amplifier also has a certain tactile quality when overdriven. Many guitarists think that the tube amplifiers respond to the guitarists “touch”, including their picking techniques and playing style, better than the solid-state amplifiers. In this respect, it is frequently stated that tube amplifiers are very touch sensitive.
There has been a long-felt need for a solid-state amplifier or signal processor that emulates the sound and feel of an overdriven vacuum tube amplifier.
A need also exists for a signal processor that emulates the sound of an overdriven vacuum tube amplifier in which the tone may be adjusted or customized to the user's desires.
Accordingly, it is a general object of the present invention to provide a new and improved signal processor that emulates the sound and feel of an overdriven vacuum tube amplifier.
Another object of the present invention is to provide a signal processor of the solid-state type that emulates the desired performance characteristics of a tube amplifier.
Yet another object of the present invention is to provide a signal processor with sound characteristics that may be adjusted to the user's tastes.
A further object of the present invention is to filter the lower frequency input signals with a second order or third order high pass filter before amplification of the input signals to reduce lower frequency intermodulation distortion when the amplifier is overdriven.
A still further object of the present invention is to provide at least two individual gain controls with overlapping gain characteristics that may be switched to provide selectable gain of those frequencies in the passband of the input filter.
Another object of the present invention is to provide related methods of filtering an input signal with an input filter of the second or third order high pass type to substantially reduce lower frequency intermodulation distortion in the signal processor.